In various applications of microfabrication technology, mechanical and electrical components are fabricated in or on a substrate such as silicon, which is part of a conventional silicon wafer. The resulting micro-electro-mechanical system (known by the acronym MEMS) is the integration of mechanical elements, sensors, actuators, and electronics on the substrate. The electronics are fabricated using integrated circuit (IC) processes, and the micromechanical components are fabricated by micromachining. Such fabrication often calls for the creation of features such as trenches or slots in the substrate. The removal of material to form such features is often carried out by etching. Moreover, other layers of material that are formed on the substrate are patterned and etched to define their final configuration.
There are a number of ways to etch silicon or other material. Irrespective of how the material is etched, it is usually desirable to determine precisely the extent of etching during and/or after the etching process.